Microwave power transmission is most often brought up in the context of solar power satellites. What about using it to transmit power across long distances on a planet's surface? Can one economically use a microwave-mirror in geostationary orbit to transmit power across hundreds of kilometers from a power station to a receiving station?

I think they did a trial in French Polynesia where they beamed power to a remote village across a difficult valley or something.

That is why I suggested geostationary satellites to reflect microwaves down to the target, somewhat like a communications satellite.

Sorry - missed that.

The issue with microwaves is you can't focus them too well. Your receiver x transmitter size needs to be on the order of 10km2 for geostationary orbit. i.e. 3km and 4km. If you can build a space mirror that big, you might as well add the panels.

It coud be a good DOD project to try this with lasers. End to end efficiency would be lousy - perhaps 10%. But that could still work for electricity in remote locations. But at 10%, solar power plus batteries are probably easier.

Out of interest, does the US military use solar power in Afghanistan? With the cost of diesel imports, it would be probably be worthwhile.

Regarding a global reflector grid, there were some papers by Komorath I believe for SSO based relay panels to allow long range transmission without new transmission line infrastructure, as a component of a large SPS fleet rollout. Whether a flat plate reflector, versus a dedicated concentrator pulling microwaves to a different transmission waveguide is appropriate is a trade study.

As for the US military, there has been research into tactical laser relay mirror systems, that use a receiver concentrator feeding a beam director for relay functions, with some testing at White Sands? The intention was a HALE UAV (blimp based?) with the relay assembly hanging underneath if I remember the diagram.

IIRC the actual "original" microwave power beaming concept was really for point-to-point transmission say from a remote nuclear power plant to a city. It was noted that there were some issues with the power beam going out to a satellite and then back down to Earth and a suggestion was made to "augment" the ground based power beam with power produced by solar electricity on the satellite which finally became straight solar power satellites.

Randy

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From The Amazing Catstronaut on the Black Arrow LV:British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Conversion to microwave is at best 65% efficient, using magnetrons. For my friend's demonstrator in La Réunion, I had recommended 2.45 GHz because cheap magnetrons exist for microwave ovens; for 2GW a tailored design would fit the preferred frequency, up to some 20GHz.

Microwaves are absorbed by bodies like birds, so their power density at Earth shall be clearly lower than Sunlight, which raises the question "why not Sun power directly". As non-thermal adverse effects are known and more may be discovered, the limit can be much lower.

The receiving rectifier can be 70% efficient, maybe 85% with efforts. At 0.01€ per 10mW, a simple diode costs its shiny penny - as much as the oceanic cable.

At each receiving antenna, you can expect to waste 10% in the sidelobes.

For 36,000 km distance and 0.02m wavelength, the antennas must have >16km2 at Earth and >0.15km2 in orbit.

We could add a few details, but these are already enough to convince me that alternative means are easier: store electricity from renewables, produce fuel from Iceland geothermy and ship it to Britain, ship paraffin molten in Iceland to warm British homes...